Polyester materials are excellent in mechanical properties, abrasion resistance, wrinkle resistance, elasticity, dimensional stability, electric insulation, chemical resistance, etc., and are widely used in the textile industry, the packaging of articles, the field of engineering plastics, and so on. However, in the process of making polyesters, diethylene glycol (DEG) by-product is unavoidably formed from ethylene glycol. The greater the concentration of DEG in the polyester, the worse the properties (such as mechanical properties, heat stability, and so on) of polyester is.
To solve such problem, many approaches are proposed, such as U.S. Pat. No. 3,749,697. It is disclosed in this U.S. patent that formation of contaminate diethylene glycol by-product during manufacture of poly(ethyleneterephthalate) prepolymer in presence of catalyst mixture is minimized by including lithium acetate dehydrate as an essential ingredient in the catalyst mixture.
In addition, U.S. Pat. No. 6,350,851 discloses a method of producing a polyester from high-purity bis-β-hydroxyethyl terephthalate as a raw material containing cations and anions in trace amounts. In the method, ethylene glycol is added as a main solvent.